Conventionally, a mercury lamp has been generally used as a backlight of a liquid crystal display. However, it is being examined due to improved luminous efficiency of an LED, an environmental problem, or the like, to change the mercury lamp to an LED light source. Particularly in a case of a liquid crystal television, a backlight that employs LEDs of three colors (red, green, and blue) has been developed because various colors can be realized with the LEDs. As a result of the development, a color sensor is used for adjustment of white balance.
The color sensor is also generally used as an image scanning device that performs (i) color adjustment of a color copying machine and a color printer, (ii) discriminant analysis of paper money, or the like.
FIG. 4 illustrates an arrangement of a color sensor 120 that is generally used.
In the color sensor 120, three P-type anode layers 111 are formed below one surface of an N-type substrate 110. Moreover, in the color sensor 120, three silicon photodiodes PD101, PD102, and PD103 are formed so as to share the N-type substrate as a common cathode layer.
In the color sensor 120, color filters 112, 113, and 114 are also formed above respective light receiving sections of the silicon photodiodes PD101, PD102, and PD103. The color filters 112, 113, and 114 together with the silicon photodiodes PD101, PD102, and PD103 are subjected to resin molding using a transparent resin 116, and a visible light transmitting filter 117 is adhered onto the transparent resin 116.
When light enters the color sensor 120, only visible light enters the color filter 112, 113, and 114 through the visible light transmitting filter 117.
Because the color filter 112 transmits only red light and infrared light, only red light enters the photodiode PD101.
Because the color filter 113 transmits only green light, only green light enters the photodiode PD102.
Moreover, because the color filter 114 transmits only blue light and ultraviolet light, only blue light enters the photodiode PD103.
Accordingly, color analysis of incoming light is possible by carrying out comparison between photoelectric currents which are outputted from the three photodiodes PD101, PD102, and PD103.
Japanese Unexamined Patent Publication No. 77507/1994 (Tokukaihei 6-77507) (published on Mar. 18, 1994) discloses a light receiving element obtained by forming an infrared cutting filter on a light receiving substrate that performs photoelectric conversion. The infrared cutting filter is a multilayer film composed of (i) a layer having a low refraction index and (ii) a layer having a high refraction index. Japanese Unexamined Patent Publication No. 223734/2000 (Tokukai 2000-223734) (published on Aug. 11, 2000) discloses a color sensor that identifies a wavelength of visible light on the basis of a bias condition.
However, in a case of the conventional color sensor 120, as illustrated in FIG. 4, which is arranged such that the visible light transmitting filter 117 is adhered onto the transparent resin 116, light does not necessarily enter the color sensor 120 through the visible light transmitting filter 117. However, light also enters the color sensor 120 from a side surface 118 of the transparent resin 116 or the like.
In such a case, light in a region other than a visible region enters the color filters 112, 113, and 114. Consequently, for example, because the color filter 112 transmits infrared light, the infrared light enters the photodiode PD101.
Although a silicon photodiode is generally very sensitive to near infrared light having a wavelength in a range from 700 nm to 900 nm, eyes of a human being cannot see infrared light.
Accordingly, a photoelectric current generated by near infrared light becomes a noise component in color analysis and interferes with a precise color analysis.
Moreover, in the conventional arrangement, the visible light transmitting filter 117 is adhered onto the transparent resin 116. This arrangement causes a problem such that the visible light transmitting filter 117 easily comes off the transparent resin 116 by mechanical or thermal stress.
Japanese Unexampled Patent Publication No. 77507/1994 (Tokukaihei 6-77507) (published on Mar. 18, 1994) neither describes nor suggests anything about a color sensor including both a color filter and an interference filter.
Japanese Unexamined Patent Publication No. 223734/2000 (Tokukai 2000-223734) (published on Aug. 11, 2000) neither describes nor suggests anything about the light receiving element provided with a combination of an interference filter and a color filter, which combination performs a color identifying function.